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What is offset printing?
Home » Office Equipment » Offset Printing » What is offset printing?Offset printing is the most commonly used printing technique in the printing industry. It is often referred to as offset lithography. The basic principle of offset printing is that ink and water do not mix. Images such as words and art are transferred to special plates which are moistened by water rollers and then by ink rollers. The paper type is normally on huge rolls of continuous paper, which is later cut and/or bound for the finished product. While the ink adheres to the image areas, the water adheres to the non-image areas. Because the water and ink do not mix, the water rollers keep the ink off of the non-image areas of the plate. This image is transferred to another surface, most commonly a rubber blanket. Then the image is transferred form the rubber blanket to paper. The name offset printing comes from the fact that the plates never touch the paper but is offset onto the rubber blankets.
Offset printing uses the four primary colors - black, cyan (blue), magenta (red) and yellow. Each color has a separate plate. The special overlay of these four colors produces the many colors you see in the final image. The eye is tricked into seeing a variety of colors by a process of dots of these four colors placed next to each other in specific patterns. Offset printing can also use premixed inks and also metallic and florescent inks. These are referred to as spot colors.
After the paper is run through the water and ink rollers, the paper is slightly wet. To avoid to risk of smudging, the paper is passed through an oven with a temperature of 350 to 400 degrees Fahrenheit. After leaving the oven, the paper is then run through chill rollers, which contain refrigerated water flowing through them. This process sets the ink into the paper so that the ink does not rub off on your hands. The entire process is a very high speed operation.
Within the offset printing market, you can choose to use the sheet-fed offset process or the web offset procedure. The sheet-fed offset process is generally used for low to medium volume jobs, which is any job that is considered to be economic for a laser printer or digital press. Web offset is for medium volume to large volume jobs and can go up to one to two million copies per job. The main difference is that sheet-fed litho machines, just as their name implies, are fed with sheets of paper. Web offset machines, which are much larger, are fed with huge reels or rolls of paper and run at higher speeds. Some of these paper reels can weigh 2,000 pounds and more. Besides the difference between the type of paper feed, the basic technology is the same. Modern offset presses are increasingly using computer to plate systems.
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